1. Field of the Invention
The present invention relates to a process for the anisotropic etching of a metal oxide coating and the simultaneous deposition of a polymer film. It is used in microelectronics and in particular in the production of display circuits for liquid crystal flat screens. The invention in particular makes it possible to produce thin film transistors based on amorphous hydrogenated silicon used in active matrix display screens.
2. Description of the Related Art
The production of thin film transistors (TFT) generally involves the production of an etching of a conductive coating or an insulating coating of metal oxide. This metal oxide etching is generally carried out by the wet technique using a solution containing hydrochloric acid heated to approximately 55.degree. C. The so-called wet methods are limited by their isotropic character, which does not make it possible to obtain well defined etched patterns having micron or submicron dimensions. It is difficult to control this type of etching.
Moreover, during the production of thin film transistors on a glass substrate, the etching of the metal oxide in an hydrochloric acid solution and, in particular, indium and tin oxide (ITO) leads to a partial etching of the glass and the migration of the chlorine ions into the glass substrate. During the production of amorphous hydrogenated siliconbased TFT's in direct contact with the glass, the migration of the chlorine ions into the amorphous silicon modifies the semiconductor properties leading to a deterioration of the electrical properties and to a limited life of such transistors.
Thus, one objective of the invention is to provide a process for etching a metal oxide making it possible to partially eliminate some of these disadvantages.
Moreover, it is known to deposit amorphous hydrogenated carbon films or polymer films on silicon or III-V material substrates by plasma assisted chemical vapour deposition process. Reference is made in this connection to the articles by R. Memming "Properties of polymeric layers of hydrogenated amorphous carbon produced by a plasma-activated chemical vapour deposition process" published in Thin Solid Films, 143, 1986, pp 31-41 and 279-289 and John J. Pouch et al "Plasma deposition of amorphous hydrogenated carbon films on III-V semiconductors" in Thin Solid Films, 157, 1988, pp 97-104 and in FR-A-2 514 743. These polymeric films are generally used as protective materials for optical or electronic components.
Moreover, it is known to etch III-V semiconductor materials by using a mixture of methane, argon and hydrogen from Electronics Letters, November 1987, vol. 23, No. 24, pp 1253-1254 "Novel process for integration of optoelectronic devices using reactive ion etching without chlorinated gas" by L. Henry et al.
In this article, reference is made to the formation of a polymer deposit during the etching of the III-V compounds and it is considered to be an unusable parasitic deposit resulting from an undesined effect and which must necessarily be eliminated in order to produce the intended semiconductor device. Reference is made therein to a number of methods for eliminating this polymeric film.